[FieldTrip] [Fieldtrip] Power spectrum units and Error in ft_topoplotER

Alessandro Orticoni alessandro.orticoni at gmail.com
Tue Sep 4 19:44:32 CEST 2018


Hi Mats,

Thanks a lot, you're right, now it works.
Yeah, I didn't apply any kind of transformation, I just used the
ft_freqanalysis and applied it to the data.

Thanks again.

Best,
Alessandro Orticoni

Il giorno mar 4 set 2018 alle ore 15:35 Es, M.W.J. van (Mats) <
M.vanEs at donders.ru.nl> ha scritto:

>
> Hi Alessandro,
>
> Power is the square of the magnitude of your signal. Since your signal is
> in uV, the units of power would be (uV)^2. Note that this only holds if you
> have not applied any transformations (like normalizations) to your raw data
> or power values. Relating to your second question, I think your
> specification of the label structure is wrong. Try replacing the first {}
> brackets in
> freq_EEG_append.label{i,1}       = freq_EEG{1}{i}.label;
> with normal brackets ():
> freq_EEG_append.label(i,1)       = freq_EEG{1}{i}.label;
>
> Hope that helps.
>
> Best,
> Mats van Es
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 3 Sep 2018 22:16:23 +0200
> From: Alessandro Orticoni <alessandro.orticoni at gmail.com>
> To: fieldtrip at science.ru.nl
> Subject: [FieldTrip] [Fieldtrip] Power spectrum units and Error in
>         ft_topoplotER
> Message-ID:
>         <
> CACwO6W8rSrzq3Vsp8sZNNvcPQ3np9cMw-tPiEBgbePPVqD5zPw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear all,
>
> I would have two questions.
>
> *1)* First one is about ft_freqanalysis: which are the units of the
> output, given the cfg.output='pow' and the EEG data in uV?
>
> *2)* The second one is about the topoplot. I'm trying to plot the power
> spectrum over the following six channels (I created the following .lay
> file):
>
> 1 -0.186808 0.232745  0.125128 0.093849 F3
> 2 0.186808  0.232745  0.125128 0.093849 F4
> 3 -0.225000 0.000046  0.125128 0.093849 C3
> 4 0.225000  0.000046  0.125128 0.093849 C4
> 5 -0.139045 -0.427979 0.125128 0.093849 O1
> 6 0.139045  -0.427979 0.125128 0.093849 O2
>
> This is the code I wrote to try to plot it:
>
> freq_EEG_append = freq_EEG{1}{1};   % Just one sleep stage
>
> for i=2:6   % Length(selchan)
>     freq_EEG_append.label{i,1}       = freq_EEG{1}{i}.label;
>     freq_EEG_append.powspctrmft_sin(i,:)   = freq_EEG{1}{i}.powspctrm;
>     freq_EEG_append.cfg.channel{i,1} = freq_EEG{1}{i}.cfg.channel; end
>
> cfg = [];
> % cfg.xlim = [0.3 0.5];
> % cfg.zlim = [0 6e-14];
> cfg.layout = 'EEGCap.lay';
> cfg.parameter = 'individual';
> figure;
> ft_topoplotER(cfg,freq_EEG_append);
> colorbar;
>
> In the first part of the code, I created the struct freq_EEG_append
> collecting the data from freq_EEG, a 1x4 cell (four sleep stages) array
> whose elements (still cell array) contains six structures (six channels),
> each resulting from the application of the ft_freqanalysis.
>
> freq_EEG_append =
>
>    struct with fields:
>    label: {6×1 cell}
>    dimord: 'chan_freq'
>    freq: [1×1121 double]
>    powspctrm: [6×1121 double]
>    cfg: [1×1 struct]
>
> But I'm getting the following error:
>
> Error using cell/unique (line 85)
> Input A must be a cell array of character vectors.
>
> Error in ft_channelselection (line 107)
> if length(datachannel)~=length(unique(datachannel))
>
> Error in ft_prepare_layout (line 234)
>   cfg.channel = ft_channelselection(cfg.channel, data.label);
>
> Error in ft_topoplotER (line 209)
> cfg.layout = ft_prepare_layout(tmpcfg, varargin{1});
>
>
> Thanks in advance for your help.
>
>
> Best,
> Alessandro Orticoni
>
>
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> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> https://doi.org/10.1371/journal.pcbi.1002202
>
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